The subject disclosure is generally directed to trapping on color printers.
Raster type printers, which have been implemented with various print engines such as electrostatographic print engines and ink jet print engines, commonly employ half-toning to transform continuous tone image data to print data that can be printed as an array of dots that can be of substantially similar size. For example, 8 bit per pixel per primary continuous tone image data can be halftoned to 4-bit or one-bit data per pixel per primary color. A frequently encountered problem in color printing is misregistration of the color planes, which can cause objectionable artifacts. For example, when black text is printed on a color background, misregistration of black relative to the other colors can cause a white gap between the black text and the color background. Other kinds of print engine problems, such as trailing edge deletion, where toner at the trailing edge fails to transfer, can cause similar artifacts. Trapping can be used to compensate for these problems by overlapping the colors near the edge so that there is no white gap when misregistration or trailing edge deletion happens. For example, the background color can be added to the black pixels near the black text edge.
U.S. Pat. No. 7,684,087 discloses a bitmap-based approach to perform black trapping. For each black pixel qualified for trapping, an algorithm evaluates pixels in each color plane that are found using the corresponding halftone screen vectors. If these pixel locations contain color, the corresponding color is added to the black pixel location. This allows the color halftone dots to extend beyond the black edges, thus eliminating white gaps according to an exemplary embodiment. Notable, the '087 patent does not control the depth of trapping and requires a relatively large number of scan lines to find neighboring cells using halftone screen vectors.
U.S. Pat. No. 8,437,045 discloses another bitmap-based approach to perform black trapping. Black trapping color image data is performed by estimating the continuous tone values associated with non-black pixels near a qualified black pixel and subsequently, the estimated continuous tone values are halftoned at the qualified black pixel locations and ORed with the original bitmap.